I found a box of C9AZ-6518-A valve spring retainer keys (picture attached), and looking at the 65-72 MPC the only application shown is for a 69/70 429 Special, which I assume is the Boss 429.

However the notes in the MPC say 1 7/32" OD - 25/64" high. I'm questioning the "1" in front of the 7/32. I would certainly think that a valve keeper would never be 1-7/32" OD, so it must be 7/32". But that seems awful small.

I checked with a micrometer and the pieces that I have match up with the 25/64" height.

But the OD can be measured at either end of the taper, and they are about 1/2" on the widest and about 13/32" at the tapered end, when two keepers are placed together.

The 428 and regular 429 MPC specs reference flange and conical IDs, which makes sense. Also the 428 provides a reference of red for color, the 429 and Boss 429 do not refer to any colors.

So the bottom line question here is, what do I have? Don't "keep" me in suspense too long if you know the answer Thanks, John